A polyimide has been widely used as a protective material or an insulating material in the electric or electronic field by virtue of its characteristics such as high mechanical strength, heat resistance and solvent resistance. Especially in an application to an alignment film to be used for a liquid crystal display device, it has been common to employ a polyimide because of the simplicity in film formation and the uniformity and durability of the coating film surface.
However, in recent years, developments in the electric and electronic fields have been remarkable, and higher properties have been correspondingly required for the material to be employed. Under these circumstances, also for a liquid crystal alignment film, it has been required to impart new properties which conventional polyimides do not have, in attempts for high densification and high performance of the displays.
One of the properties required for a liquid crystal alignment film is an ability to provide a high pretilt angle. As a means to obtain a high pretilt angle required for a polyimide liquid crystal alignment film, JP-A-64-25126 and JP-A-5-27244 propose a treating agent for liquid crystal alignment comprising a polyimide precursor or a polyimide having a side chain, prepared by using, as a material, a diamine having a long chain alkyl group, etc. However, the diamine proposed in these references, has had a problem with respect to the low level in efficiency to increase the pretilt angle relative to the amount introduced, or in the reactivity.
When properties other than the pretilt angle, are also to be imparted to the liquid crystal alignment film, the amount of the diamine introduced to increase the pretilt angle should better be small, as the degree of freedom in polymer design will thereby be broadened. However, if the amount the diamine introduced, is too small, it becomes impossible to secure the required pretilt angle.
Further, in a case where a very high pretilt angle of from 20° to 90° is required, it is necessary to introduce a large amount of a diamine to increase the pretilt angle. Accordingly, if the reactivity of the diamine is low, it takes time for the polymerization of the polymer, or in some cases, polymerization may not substantially proceed. Taking time for the polymerization is industrially problematic, and if the polymerization degree of the polymer is inadequate, such will be a problem from the viewpoint of the durability as a liquid crystal alignment film.
In view of the above problems, the present invention is to provide a novel diamine compound which is highly effective to increase the pretilt angle even in a small amount and excellent in the polymerization reactivity, a polyimide precursor or a polyimide synthesized by using such a diamine compound as a part of the material, and a treating agent for liquid crystal alignment containing such a polymer.